Method fob dewaxing oils



E. W. GARD METHOD FOR DEWAXING OILS Aug. 9, 1938.

Original Filed Aug. 2l, 1935 vm ww b Qm.

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Ressued Aug. 9, 1938 UNITED STATES PATENT OFFICE METHOD FOR DEWAXINGOILS Earle W. Gard, Palos Verdes Estates, Calif., as-

signor to Los Angeles,

Union Oil Company of California,

Calif., a corporation of California original No. 1,989,355, datedJanuary 29, 1935,

Serial No. 686,016, August 21, 1933.

Application for reissue March 13, 1937, Serial No. 130,753

16 Claims.

The present invention relates to a process for the separation frompetroleum of those hydrocarbons which are normally solid at ordinarytemperatures. In accordance with this process, I am able to separatefrom petroleum or mineral oil such substances as paraffin, crystallineor amorphous wax or gummy or resinous substances which may be present.While the invention is particularly adapted to the removal of paraffin,amorphous or crystalline wax or gummy or resinous substances frompetroleum residues to produce lubricating oil, it may be utilized in thetreatment of any other petroleum fractions where it is desirable toseparate the oil from the foregoing substances.

Many crude oils from which lubricating oil is produced contain parain orwax. It is found associated with lub-ricating oil fractions of paraffinbase crude oil and also with lubricating oil fractions produced from anyof the mixed base and asphalt brase crude oils. The presence of Wax inlubricating oil is not only of doubtful value but also limits thetemperature at which lubricants containing it may be used because ofcongclation at low temperatures. Therefore, in the production oflubricating oils from petroleum fractions containing wax or paraffin, itis customary to remove a substantial portion of the wax or paraflinpresent in the oil in order to lower the temperature at which thelubricant congeals. The temperature at which an oil congeals is commonlyreferred to as its pour point and this value is usually obtained,according to Method D-91-3O outlined by the American Society forTesting Materials.

One of the more successful processes suggested for the production oflubricating oil from petroleum fractions or residues which containsubstances congealing at low temperatures as set forth above and towhich I shall hereinafter refer as wax, consists in rst diluting the Waxcontaining oil with a light hydrocarbon solvent such as one which isvaporous at normal temperatures and pressures as, for example, propane,under a pressure sufficient to maintain the solvent in its liquid stateand subsequently chilling the solution to effect precipitation of thewax. This mixture is subjected to settling, centrifuging or filtrationfor the purpose of removing the precipitated wax from the solution ofoil and solvent. The oil solvent solution is then heated to vaporize thesolvent from the oil.

The present invention relates to an improvement on the aforesaid processwhich has several advantages over other known processes for theseparation of waxes. For example, the use of a light diluent such aspropane, lowers the viscosity of the chilled mass sufficiently tofacilitate the separation of the precipitated wax from the chilledsolution of propane and oil. Another advantage of using this type ofsolvent as a diluent for the oil containing wax is that by allowing Aaportion of. the solvent to vaporize under reduced pressure, thenecessary refrigeration is obtained to chill the oil to the desireddewaxing temperature. The waxy oil is first dissolved under pressure inthe light liquid hydrocarbon and then a portion of the light liquidhydrocarbon is vaporized or allowed to boil off at reduced pressurewhich thereby lowers the temperature of the waxy oil dissolved in theremaining solvent to a point sufliciently low to precipitate the wax.Thus, the light liquid hydrocarbon functions both as a diluent for thewax bearing oil and also as an internal refrigerant to chill thesolution of oil and wax to the proper dewaxing temperature. Furthermore,this internal refrigeration may occur in the propane itself prior to itsintermixture with the oil and Wax.

The objection to the foregoing process has been that unless extremelylong settling periods are provided, a portion of the wax is carried overwith the oil solvent solution decanted from the wax settling chamber. Ihave observed in the foregoing process that a portion of the waxprecipitated, that is, released from solution by refrigeration, settlesrapidly and in a relatively short time, while the remaining portion ofthe wax remains in a cloudy suspension in the solution of solvent andoil and requires considerable time to settle. This is due to thedifferent physical characteristics of the twotypes of wax. The firstportion of the wax which settles rapidly to the bottom of the settler ordecanter is a hard, heavy and solid wax. It is granular `and crystallineand has a larger particle size than the remaining Wax in suspension. Theremaining portion of the wax is soft and slime-like and is in so fine aform of subdivision that filtering or settling is substantially impeded.This type of wax is in the nature of a gel or slime and as such offersmany difliculties in its removal from the chilled solution of oil andsolvent. The slimy wax forms an impervious layer upon the filter plateof the filter press which obstructs free movement of the dewaxed oil.Furthermore, the Wax flocks or aggregation which are formed during thechilling opera-tion will not readily settle out by cold settling even inthe presence of propane which increases the difference in specic gravitybetween the solution of oil in the solvent and wax.

Thus, after a certain time of settling, there appears to be threedistinct stratified layers, the rst comprises the hard granular waxwhich settles rapidly to the bottom of the settler. Superimposed on thislayer is a strata of oil and solvent containing the fnely divided wax insuspension and above this is a clear solution of oil and solventsubstantially free from either type of wax. In decanting the supernatantsolution of oil and solvent substantially free from wax, there is atendency for the middle layer containing the fine wax in suspension tobe carried over with the oil solvent solution. The present process isaimed at the prevention of this occurrence. I have discovered that if aportion of the middle layer of oil solvent solution containing thefinely divided wax in suspension is continuously withdrawn from thesettling chamber, the tendency for the nely divided wax to be carriedinto the upper strata and thus decanted with the clear oil solventsolution is obviated. If the withdrawn portion is passed to the streamof oil entering the treating process and commingled therewith, the waxwill also be commingled with the naturally occurring Wax of the oilstream and will re-precipitate in the subsequent chilling of the oilsolvent solution. When the chilled mixture is again passed into thesettler, there will be present a larger proportion of wax so that aconsiderably vlarger amount of the wax will settle to the bottomrapidly, since the amount of wax settling rapidly to the bottom of thedecanter is dependent upon the percent of wax in the mixture and themanner in which it was precipitatedl from solution. By the latterstatement is meant that by shock chilling or rapid cooling of thesolution of oil, wax and propane, a large proportion of the wax Willprecipitate in a form too finely divided for ecient settling and/orfiltration. If the solution is cooled or chilled slowly to the nal lowtemperature, suincient time is allowed to permit the wax crystals torecrystallize and grow, the crystals formed in the earlier stage ofcooling at the higher temperature that is, before the nal lowtemperature of aproximately 40 F. is reached, form nuclei for thefurther development of crystals in the later stage of cooling to lowertemperatures. I prefer to include this type of cooling in combinationwith other features of my invention, although I do not necessarilydesire to be limited thereby. However, no matter how slowly the mixtureof oil, wax and propane is cooled, there is inevitably a portion of thewax which remains in suspension in finely divided form and whichrequires considerable time to settle. This portion of the wax remains inthe middle strata in suspension and when the oil solvent solution isd-ecanted from the settler a portion of the nely divided wax is carriedo-ver with the oil solvent solution and thus the pour point of thelubricating oil is increased to a certain extent.

The precipitation of the mixture of oil and added wax will cause more ofthe finely divided wax to precipitate as such due to the added amountbut the higher concentration of this nely divided wax will tend towardsthe agglomeration into larger particles which will then more readilysettle to the bottom of the settler.

From the above discussionI it is apparent that the present inventioncomprises, in part, a continuous withdrawal of the solution of nelydivided wax, oil and solvent at a point above the bottom outlet of thesettling chamber and below the inlet of the charge of chilled oil,solvent and wax and commingling with the withdrawn mixture with the oilentering the process and subsequently chilling the mixture of oil andadded wax to precipitate both the wax present in the oil and that addedthereto.

When the term light liquid hydrocarbon is employed herein, I intend toinclude those hydrocarbons which are normally in the vapor state atatmospheric temperature and pressure. Such hydrocarbons include methane,ethane, propane, iso-butane, butane and mixtures thereof. These may beobtained by rectification of casinghead gasoline by the so-calledstabilizing method. 'I'hey are the overhead thus obtained. They areliquefied by compression and cooling in the conventional manner and aredrawn on" into pressure chambers where` they are maintained in theliquid state until they are used. A typical analysis of Such a fractionis 6.72% ethane, '72.2% propane, 19.91% iso-butane and 1.17% normalbutane. It Will be understood, however, that this merely illustrates thetype of fraction which may be used and that the composition may vary.Since the preponderant member of this fraction is propane, I will referto this fraction as propane or liquid propane for purposes of.simplicity.

With the above discussion in mind, it will be perceived that it is afurther object of my invention to provide a process for the separationof wax from oil in the production of lubricating oil wherein the oil ismixed With a hydrocarbon solvent and the mixture chilled to precipitatewax. The chilled mixture is allowed to settle so as to permit wax tosettle and a portion of the solution containing wax above the bottomoutlet of the settler is withdrawn and returned to the oil entering theprocess.

It is an object of my invention to prevent the carrying over of nelydivided wax with oil in the decantation of. a settled solution of oil,solvent and precipitated wax by continuously or intermittentlywithdrawing a portion of the solution of oil and solvent containingfinely divided Wax from the settling chamber at a point above the strataof more readily settling wax.

Another object of my invention resides in concentrating the oil enteringthe process for wax separation with finely divided wax separated duringthe settling of the chilled solution containing precipitated wax.

Other objects and advantages of my invention will be apparent from thefollowing description of my invention taken from the drawing whichrefers to a schematic arrangement of apparatus for carrying out myinvention:

Referring to the drawing, a wax or an asphalt and Wax containing oilsuch as a residuum obtained from topping of a Santa Fe Springsl crudeoil to such extent as to leave fractions in the residue having aviscosity of 40() to 500 seconds Saybolt universal at 100 F. is takenfrom tank l and is withdrawn into line 2 by pump 3 passed into line 4where it meets a stream of liqueed normally gaseous hydrocarbon solventsuch as liquid propane taken from storage tank 5 via line 6 and pump 1which forces the liquid propane through valve 8 into line 4. The amountof propane introduced into line 4 will depend upon the character of theoil and the temperatures desired i'n the chilling column 46 and alsoupon the amount of solvent desired in the settling chamber 55. v Thus,the amount of solvent to be mixed with the oil should be suicient toeilect the desired chilling temperature by evaporation of solvent byrelease of pressure and to provide sufficient solvent in the chilledmass to provide for good and eflicient settling in of the precipitatedwax. In the latter operation the amount of solvent should not be lessthan approximately 4 volumes of solvent to 1 volume of oil. In general,an initial volumetric ratio of approximately 7 to 10 volumes of solventto 1 volume of oil will be suicient to effect the desired lowering oftemperature and to provide for eicient settling. However, a lowervolumetric ratio may be employed, that is, merely suicient to effect thedesired reduction in temperature and then the mass may be supplementedwith further quantities of solvent to bring the ratio up to 4 to l inthe settling operation.

The mixture of liquid propane and oil containing asphalt and wax ispassed through turbulence or mixing coil I0 into a decanter or asphaltprecipitator II where the oil containing asphalt is precipitated andsettles rapidly as a slurry of substantially pure bitumen or hardasphalt containing some oil and propane. The amount of propaneintroduced into the oil will also depend upon whether the oil containsasphalt or not. If it contains asphalt and it is desired to remove theasphalt at the bottom of the decanter II as a slurry of asphalt andpropane, that is, as a mixture of substantially pure bitumen or hardasphalt and propane or as a liquid fraction of an asphalt containingpropane and some oil and thus leave a portion of the asphalt in the oilsolvent solution to act as nuclear bodies for the wax in the subsequentprecipitation of wax by chilling. If it is desired to separate theasphalt as a liquid fraction, the volumetric ratio of propane to oilwill be within a range `of 0.6 to 6 to 1 depending upon the character ofthe oil and the degree to which it was topped. Higher volumetric ratioswill precipitate the asphalt as a slurry of substantially pure bitumenand propane. It is preferable to remove as much Aof the asphalt presentin the oil as possible in the decanter II and, therefore, it isnecessary to employ high volumetric ratios in general from '7 to 10volumes of propane to 1 volume of oil to accomplish this effect. Apressure of approximately 125 to 175 pounds per square inch gauge and atemperature of about '70 F to 80 F. is maintained in the decanter orasphalt precipitator II. The pressure in decanter I I is controlled bymeans of equilibrium line I2 controlled by valve I4 and connected to thehigh pressure propane storage tank 5.

The asphalt precipitated in decanter II is withdrawn via line I5controlled by valve I6 and is forced by pump I1 under pressure throughheating coil I8 Where it is heated to a sufficiently high temperature tomelt the asphalt and vaporize residual propane. The heated mixture isthen passed through line I9 and ilashed to pressure reduction valve 20into evaporator 2| which is operated at a lower pressure. Evaporator 2|is provided with mist extractor 22 and with a perforated pipe 23controlled by valve 23 through which superheated steam is introduced tosupply additional heat and to reduce the asphalt to the properspecication, generally, only as regards flash and fire points. Theoverhead from evaporator 2I ypassing through extractor 22 is sentthrough line 24 controlled by valve 24 to cooler 25 and then via line 26to separator 21. The uncondensed propane from separator 21 is sentthrough line 28 controlled by valve 29 into line 30 to the suction ofcompressor 3I where its pressure is raised to that in the high pressuresystem and is then sent via line 32 to cooler 33 where it is liquefiedand then runs down vla line 34 into propane storage tank 5. Anycondensed light oil in separator 21 is withdrawn through line 35 andcondensed water through line 36. Ihe asphalt is taken from the bottom ofevaporator 2I and sent through line 38, controlled by valve 39 andpumped by pump 40 into storage tank 4I.

The overflow from decanter II consisting of propane and oil free fromasphalt but containing the wax in solution is sent through line 43 bypump 44 through pressure reduction valve 45 into decanter or chillingcolumn 46. In chiller 46, suicient propane is permitted to vaporize toreduce the temperature of the remaining material to a sufficiently lowtemperature which causes Wax to precipitate from solution. It ispreferable to gradually lower the temperature to a dewaxing temperatureand to avoid shock chilling. The preferable rate of temperaturereduction should not exceed 4 F. per minute. The temperature reductionis effected by gradually reducing the pressure in the column 46 by theproper operation of valve 48 on line 41 and cornpressor 3I which isconnected to the column by lines 41, 4S and 30. The pressure will begradually lowered to about 0 to 25 pounds gauge which corresponds to atemperature of approximately 40 F. to 0 F. The propane evaporating incolumn 46 is passed out of the top through line 41 controlled by valve48 and then passes into lines 49 and 39 to the suction of compressor 3|where the vapors are compressed, liqueed in cooler 33 and passed tostorage tank 5.

Due to the fact that sufficient time must be given to gradually chillthe oil and solvent passing into the chiller 46 and to make the processcontinuous, a plurality of chilling colums like that shown at 46 may beprovided and separated alternately. However, in batch operation merelyone of such chilling columns will be sufficient. In such case, theentire material from decanter II may be transferred into column 46 andthe chilling accomplished by controlling the operation of valve 48 online 41.

The chilled charge in column 46 comprising oil, propane and precipitatedwax is withdrawn from the bottom via line 5I controlled by Valve 52 andpumped by pump 53 via line 54 into a settling device 55. In settler 55 aportion of the precipitated wax settles rapidly to the bottom of thesettler, while the more flocculent', light and finely divided wax willrequire considerable longer time to settle. It is preferable that theintroduction of the mixture via line 54 into the settler be at a pointat or above the point where the fine wax remains in suspension in themixture. This will prevent the fine wax from being carried over with theoil.

The ne wax in suspension is withdrawn from the settler 55 at a pointbelow the inlet 54 as a mixture of wax, propane and oil. 'This mixtureis withdrawn via either of lines 56 controlled by valves 51 and pumpedby pump 58 into line 59 provided with by-pass valve 60 and passed toline 4 where it is mixed with the oil being treated. If desired, the waxin the mixture may be melted by closing valve 60 and opening valve 6I online 62 and is then passed through heater 63 where it is heated toapproximately atmospheric temperature or higher to melt the wax andpassed via line 64 into line 65. If desired, ay portion of the mixturemay be by-passed through heater 63 and the remaining portion passedthrough valve 60 and the mixture commingled in line 65. The admixture ofthe heated portion with the unheated portion passed through valve 60will bring the mixture to the proper temperature for admixture With theincoming oil. It is preferable to continuously withdraw the solutioncontaining the fine wax via line 56 so that an equilibrium is maintainedin the settler 55 and thus prevent the passage of the fine wax frombeing carried over into the oil-propane phase.

The precipitated wax at the bottom of settler 55 is withdrawn by meansof gear pump 61 and passed into line 68 controlled by valve 69 and thenthrough heater 'Hl where it is heated to a temperature suflicient tomelt the Wax and vaporize residual propane. 'I'he heated mixture is thenpased via line 1| into separator 'l2 where vaporized propane is removedby line 13 controlled by valve 14, cooled in cooler 'l5 and passed vialine lli into line 30 to the suction of compressor 3| where its pressureis raised, condensed in cooler 33 and then passed into propane storagetank 5. The Wax is Withdrawn from the bottom of separator 12 via line 11controlled by valve 'I8 and pumped by pump 19 into storage tank 80.

The overflow from settler 55 free from wax is withdrawn via line 8| andpumped by pump 82 through valve 83 into heater 84 provided with mistextractor 85 where the propane present in the oil is vaporized by theaid of steam circulated through closed steam coil 86. The vaporizedpropane passes out of the heater through line 81, controlled by valve88, cooled in cooler 89 and then passes through lines 9U, 49 and 30 tocompressor 3| then through cooler 33 into propane storage tank 5. Thedewaxed propane-free oil passes from the heater 84 by means of line 9icontrolled by valve 82 and pumped by pump 93 through line 84 intostorage tank 95. This oil may be subjected to the conventional acidtreatment followed by neutralization and water washing. If desired, thesolution of oil and propane removed from decanter I I may be'acidtreated and neutralized prior to separation of the wax, or the solutionof propane and oil free from Wax withdrawn from the settler 55 may belikewise treated prior to the separation of the residual propane.

It is to be understood that the above is merely illustrative ofpreferred embodiments of my invention of which many variations may bemade by those skilled in the art without departing from the spiritthereof.

I claim:

1. A process for dewaxing oil which comprises mixing said oil containingwax with a light hydrocarbon diluent, chilling said oil diluent solutionto precipitate wax comprising a mixture of more readily settling wax andless readily settling Wax, settling the cooled mixture to eilectseparation of precipitated wax, withdrawing oil diluent solutionsubstantially free from precipitated wax from the upper part of thesettling zone, withdrawing settled Wax from the lower part of said zoneand simultaneously with the withdrawal of said substantially wax-freeoil diluent solution, withdrawing oil diluent solution containingunsettled wax from a point intermediate said upper and lower parts ofthe settling zone under such conditions as to prevent the unsettled waxfrom being carried over into the oil diluent solution substantially freefrom precipitated Wax.

2. A process as in claim 1 in which the withdrawn oil diluent solutioncontaining unsettled wax is returned to the oil to be dewaxed.

3. A process as in claim 1 in which thewithdrawn oil diluent solutioncontaining unsettled wax is heated and returned to the oil to bedewaxed.

4. A process as in claim 1 in which the diluent comprises a liquefiednormally gaseous hydrocarbon.

5. A process as in claim l in which the diluent comprises propane.

6. A process for dewaxing oil which comprises mixing said oil containingwax with a light hydrocarbon solvent, chilling said oil solvent solutionto precipitate said wax, said precipitated Wax comprising a mixture ofmore readily settling wax and less readily settling wax, passing saidoil solvent solution containing said precipitated Wax into a settlingchamber, settling said precipitated wax from said oil solvent solutionin said settling chamber to permit said more readily settling wax tosettle at the bottom of said settling chamber and to permit said lessreadily settling wax to remain in suspension in said oil solventsolution above said more readily settling wax, and continuously removingoil solvent solution containing said less readily settling wax from saidsettling chamber during said settling under such conditions as toprevent the less readily settling wax from being carried over into oilsolvent solution substantially free from precipitated wax.

7. A process as in claim 6 in which the withdrawn oil solvent solutioncontaining unsettled wax from the point intermediate the upper and lowerparts of the settling Zone is returned to the oil to be dewaxed.

8. A process as in claim 6 in which the withdrawn oil solvent solutioncontaining unsettled wax is heated and returned to the oil to bedewaxed.

v9. A process as in claim 6 in which the diluent comprises a liqueednormally gaseous hydrocarbon. Y

10. A process as in claim .6 in which the diluent comprises propane.

11. A process for dewaxing oil which comprises mixing said oilcontaining wax with a light hydrocarbon solvent, chilling said oilsolvent solution to precipitate said wax, said precipitated waxcomprising a mixture of more readily settling wax and less readilysettling wax, passing said oil solvent solution containing saidprecipitated wax into a settling chamber stratifying said oil solventsolution containing precipitated wax in said settling chamber into threelayers, an upper layer of oil and solvent substantially free from wax, alower layer of the more readily settling wax, and an intermediate layerof oil and solvent containing said less readily settling wax,withdrawing said upper layer of oil and solvent from said settlingchamber and simultaneously with the Withdrawal of said substantiallywax-free oil solvent solution, withdrawing said intermediate layer ofoil and. solvent containing said less readily settling wax from saidsettling chamber under such conditions as to prevent the less readilysettling wax from being carried over into the oil solvent solutionsubstantially free from precipitated wax.

12. A process as in claim 11 in which the diluent comprises a liqueednormally rgaseous hydrocarbon.

13. A process as in claim 11 in which the diluent comprises propane.

14. A process as in claim 11 in which the intermediate layer containingthe unsettled wax is returned to the mixing chamber.

15. A process as in claim 11 in which the intermediate layer containingthe unsettled wax is heated and returned to the mixing chamber.

16. A process for dewaxing oil which comprises passing a stream of oilcontaining wax into a mixer, commingling said oil in said mixer with aliqueed normally gaseous hydrocarbon solvent, chilling said oil solventsolution to precipitate wax, said precipitated wax comprising anlixtureof granular and more readily settling wax, and nely divided and lessreadily settling Wax, passing said oil solvent solution containing saidprecipitated wax into a settling chamber, and in said settling chamberconcentrating said finely divided wax in said oil solvent solution as anintermediate layer between a bottom layer of more readily settling waxand an upper layer of oil and solvent substantially free from wax,decanting said upper layer of oil and solvent from Said settlingchamber, and continuously withdrawing said concentrated intermediatelayer of oil and solvent and finely divided wax from said settlingchamber under such conditions as to prevent the finely divided wax frombeing carried over into the solution of oil and solvent substantiallyfree from precipitated wax.

EARLE W. GARD.

